We assessed vagal tone changes during an attention demanding CPT task in 12 boys (mean age 9 yrs, 5 mos) exposed prenatally to opiates and 12 (mean age 9 yrs, 10 mos) male controls. Mothers of opiate-exposed and control boys were primarily single and of lower income. Groups did not differ significantly on mother's education, income, or marital status. Racial composition of the groups also did not differ (opiate-exposed: 8 black, 4 white, controls 7 black, 5 white). Vagal tone was measured pre- and post-baseline and during the 3 tasks of the Gordon Diagnostic System. Vagal tone is a heart rate variability measure that quantifies parasympathetic inhibition of the heart. Results indicated that opiate-exposed boys failed to suppress vagal tone compared to control boys when distractors were added to a vigilance task (p .05). In normal children and adults, vagal tone is suppressed during tasks requiring sustained attention. These preliminary results indicate that normal physiological responses to increased attentional demand may be impaired in opiate-exposed boys in this age range. These physiological response patterns were not associated with prenatal alcohol, nicotine, or marijuana exposure in these samples. The design of this study does not distinguish among genetic, teratogenic, or child-rearing practice effects. Further research is needed to replicate and extend these findings as a possible risk factor for subsequent drug abuse in children exposed prenatally to opiates.